Pressure-sensitive adhesives are extensively used in masking tapes, double-faced pressure-sensitive adhesive tapes, surface-protective films, packaging tapes, and the like. Developments in pressure-sensitive adhesives of the aqueous dispersion type containing no organic solvent have hitherto been proceeding from the standpoints of a measure for environmental preservation, resource saving, safety, etc., and the amount of the aqueous dispersion type pressure-sensitive adhesives to be used tends to increase. Of such aqueous dispersion type pressure-sensitive adhesives, rubber-based pressure-sensitive adhesives of the aqueous dispersion type are most extensively used at present as they have advantages such as reduced limitations on adherend selection and excellent low-temperature adhesiveness. Acrylic pressure-sensitive adhesives of the aqueous dispersion type are coming to be widely used in place of the conventional rubber-based pressure-sensitive adhesives of the aqueous dispersion type because of their excellent adhesive properties, weatherability, etc.
On the other hand, masking tapes, for example, have had the following problem. When a masking tape, which is a tape for masking adherends on the occasion of painting, sealing or the like, is applied in the rainy season or low-temperature winter season to an adherend surface where dew condensation has formed, sufficient adhesive force sometimes cannot be obtained at the time of its application and the tape shifts or peels, resulting in poor workability.
Double-faced pressure-sensitive adhesive tapes and the like also have had the same problem in application to dewy surfaces.
A pressure-sensitive adhesive tape containing a water-soluble polymer as a major component has been disclosed as an adhesive tape having good adhesiveness to dewy surfaces.
However, satisfactory results have been unobtainable because low-molecular weight components, which have been dissolved away as a result of water absorption/swelling, cause fouling upon peeling, the adhesive's insufficient cohesive force leaves adhesive residues upon peeling, and so on.
Further, as a pressure-sensitive adhesive which exhibits excellent adhesiveness in humid places or when applied to surfaces covered with water, frost, ice, etc., the one comprising an acrylic acid ester copolymer obtained by emulsion polymerization and a specific amount of a polyethylene glycol having a weight average molecular weight of from 180 to 1,100 is known (cf. Japanese Patent Laid-Open No. 227682/1988). However, there has been a problem that the pressure-sensitive adhesive comprising such components as above can not give sufficient initial pressure-sensitive adhesive force toward dewy surfaces, and so on.
In addition, when a masking tape is applied on an adherend and left as it is for several days, peeling slowly starts from the end of the tape (constant-load peeling property) during this period. This has been a problem of poor workability upon restarting the work.